Hydronic radiant heating is one of the oldest known forms of floor heating in the world, having its origins in ancient Rome. Radiant heating came into widespread use in the U.S. during the post-World War II building boom. Modern radiant systems include underfloor heating systems, wall-heating systems, and radiant ceiling systems.
Conventional household heating and cooling systems are based on forced convection heating, wherein system-generated air convection currents circulate through the home and regulate air temperature. Radiant heating and cooling systems utilize the principle of radiant heat transfer a more efficient form of transferring heat.
The earth is warmed by heat radiation through radiant heat transfer. All non-reflective bodies in the path of this radiation exchange thermal radiation continuously, and have their temperature elevated by absorption of the radiation. This fact is appreciated when one feels the thermal comfort of the sun on an otherwise lower ambient temperature day. Likewise, greenhouses capture radiant energy from the sun, withholding more energy than escapes.
In a radiant heating system, a heat transfer plate on the radiant panel acts as the sun heating the Earth in the above example. Thus, radiant systems heat people and objects directly, as opposed to merely the air space around the people and objects as in conventional household heating systems. Indirectly, the air temperature in a radiant heating or cooling system is changed as well. To effectuate this transfer of heat, the radiant system has radiant panels which in turn have embedded within them hydronic tubing or electric conduits that alter the temperature of a heat transfer plate. In a warming system, resistance within the electric circuit, or warm water flowing through the hydronic tubing warms the heat transfer plate (generally a large flat panel) through conduction, which in turn radiates heat energy to a living space. In systems where the heat transfer plates are concealed behind an object such as drywall, the heat transfer plate passes heat to the object through conduction that in turn radiates heat to the living space. In some installations, the heat transfer plate is omitted and the electric circuit or hydronic tubing is simply placed behind the walls, warming the walls directly.
The Applicant's invention relates specifically to the hydronic tube type radiant heating and cooling systems. In hydronic radiant systems, tubes in direct mechanical contact with the panels carry heated water. The choice of liquid used is dependent on factors such as corrosiveness of the liquid, resistance to contamination, filtration, freezing temperature, and evaporation.
In hydronic radiant cooling systems chilled water is circulated through the hydronic tubes. The cooling occurs in water chillers, heat pumps, condensing units with heat exchangers, evaporative cooling towers, evaporative “night sky” cooling, or in some cases even naturally cool ground water can be used. The cool water chills the radiant panels that absorb heat from the living space.
Heat transfer plates may be integrated into ceiling units, may be recessed, embedded in the floor or ceiling, or may be surface-mounted. The plates may be either concealed or visible. The plates are often concealed behind drywall or under floorboards to give the appearance of a normal floor, wall or ceiling. The type of application generally determines the type of plate to be used. For instance, discrete-metal or framed-fiberglass modules are commonly used in T-bar grid ceiling heating installations.
In concealed overhead ceiling installations, heat is ideally efficiently transferred to the ceiling itself, which in turn acts as the radiant energy delivery surface. Similarly, in a wall concealed installation the wall itself acts as the radiant energy delivery surface and in a floor installation the floor acts as the energy delivery surface. Visible designs are generally steel or aluminum linear plates that are mounted directly on the ceiling surface. Visible designs installed in T-bar grid ceiling systems are generally modular panels having flat, grooved, or channeled surfaces.
The benefits of radiant heating and cooling systems over conventional systems are that the radiant systems heat and cool with fewer areas of unevenness, heat and cool with increased efficiency, and do so without human-detectable noise. Uneven heating/cooling and noise have traditionally been problems in a traditional air convection heating and cooling system. Further, because there is no significant air movement in a radiant heating or cooling system, the movement of dust, dirt, pollen, bacteria and other germs is dramatically reduced. Because radiant heating systems warm the objects in a room directly (as opposed to merely warming the air that flows over them), heat loss from openings in the room to be heated is less of an issue than in systems that merely heat or cool the air. Perhaps the most important benefit lies in the energy saving through the use of these systems. In contrast to air handling systems, radiant heating and cooling systems typically utilize 30% less energy (based on title 24 analysis of three identical houses using each method) to produce the same or better level of comfort for the house's inhabitants.
Despite the many benefits of radiant heating and cooling systems, there are still problems hindering their widespread adoption by consumers. One drawback involves the placement of the hydronic tubes used to deliver heat energy to and pull heat energy from the room being temperature regulated. These tubes are generally concealed behind the walls or ceiling of the room being regulated. Hence, there must be a space to accommodate them. In many installations, such as standard T-bar ceiling installations, space is not tight and thus is not an issue. In still many other installations, some offset must be provided to the wall or ceiling to leave space for the placement of the hydronic tubing.
Problems in the past faced by installers of hydronic radiant heating and cooling systems, and homeowners using such systems are related to the shape of the heat transfer plates typically nailed or screwed to ceiling joists, or to studs in a wall. By affixing flat heat transfer plates directly to the joists or studs, there is no space behind the plate (opposite the living space side) for the hydronic tubing, which is typically much thicker than the plate itself. Thus, to place the hydronic tubing on the side of the heat transfer plates facing away from the living space, holes must be drilled in the joists or studs through which the tubing may pass. This occurs numerous times in each room in which the system is installed, increasing labor and costs. Additionally, this installation often requires the hydronic tubes to be bent away from the heat transfer plate and around the joists or studs, or away from the heat transfer plate and through the holes drilled in the joists or studs. This can put tension on the radiant panels and can cause the edges to warp up and away from contact with the drywall. This warping decreases the size of the contact patch between the heat transfer plate and the ceiling or drywall to which the heat is transferred through conduction, thus degrading the overall efficiency of the system.
A problem related to heating and cooling systems in general relates to energy use. Due to rising oil and electricity costs, many of the most recent innovations in air conditioning technology have placed an emphasis on energy efficiency. While radiant heating and cooling systems utilize 30% less energy than conventional heating and cooling systems (see above), there remains room for improvement. For instance; in a radiant heating system, much of the heat not transferred to the living space simply remains as energy in the heated liquid in the hydronic tubing. In a cooling system, cool water is returned. Energy losses occur in the system through less than perfect conduction transfer between the hydronic tube and the radiant panel, through mechanical losses by the pumping process, and through radiant and conductive losses through the supply and return piping itself.
In a ceiling installation, relatively large amounts of energy are lost as a result of intermittent contact between the heat transfer plate and the drywall. A common current approach to radiant floor systems is generally known as the stapleup method. Here, the hydronic tubing is suspended on plastic stand-off clips about half an inch from the joist. No emitter plates are used. In a heating system, the water is circulated at a very high temperature, and warms the air in the floor cavity, which in turn warms the floor. This inefficient heat transfer process works well when there is very good insulation under the entire assembly, as the heat generated migrates into the floor and warms the house, instead of out to the subfloor space. Transfer of heat in these floor systems and in general for any installation is increased through good mechanical contact between the radiant panel and the floor or drywall that is exposed to the living space.
A second main source of inefficiency relates to the emissivity and conductance on each side of the heat transfer plate. Ideally a radiant panel assembly will efficiently transfer energy from the heat transfer fluid to the hydronic tube thence to the heat transfer plate and to the drywall while not losing any heat to the backside of the radiant panel. Heat transferred to the backside of the panel (away from the living space) is generally an inefficient use of energy.
An additional problem occurs in floor installations. In these installations, the heat transfer plates and associated hydronic tubes are subjected to far more stress than they are subjected to in a ceiling installation. For instance, furniture may be placed on top of the panel after installation, and it is very likely foot traffic will occur over the installation. These crushing forces can damage the panels, the tubes or both.
To offset expected heat loss in a radiant panel heating system, the temperature of the circulating liquid is increased. However, a similar solution (lowering the temperature of the circulating fluid to offset the expected heat loss) is not feasible in radiant cooling systems, because once the temperature of the liquid is decreased by too much, condensation can occur, damaging the building or home in which the system is installed. Efficient pumps and well insulating piping can mitigate some of these losses, but larger efficiency results are generally obtained through measures taken near the radiant panel itself.
There is thus a need to further improve the efficiency of radiant heating and cooling systems, and a need to ease the installation of such systems by avoiding the need to drill holes through joists or studs.
It is thus a first objective of the present invention to provide a heat transfer plate that obviates the need to thread the radiant panel system hydronic tubes through the joists in a ceiling or studs in a wall.
It is a second objective of the present invention to provide a heat transfer plate for floor, ceiling, or wall installations that provides efficient transfer from heat from the panel to the floor or ceiling, both through a large contact point between materials through which heat is conducted and through a radiant panel having a low emissivity coating on the side facing away from the living space and a high emissivity coating on the side facing towards the living space.
It is a third objective of the present invention to provide a sturdy floor installation solution for radiant panel installation that will allow the radiant panels and associated hydronic tubes to withstand the crushing forces associated with this type of installation.